1. Field of the Invention
The present invention relates to a magnetic driver suitable for a shutter device or aperture device to be incorporated into an image sensing apparatus such as a video camera, a film-based camera, or a digital still camera, or suitable for an optical filter driver.
2. Description of the Related Art
A rotary actuator described in Japanese Patent Laid-Open No. 10-248231 is conventionally known as a cylindrical rotary actuator incorporating a coil in the direction of the rotating shaft of a magnetized rotor magnet.
This rotary actuator is characterized by including
a rotor made of a permanent magnet,
a main body case, which is made of a nonmagnetic material and accommodates the rotor by supporting it such that it can rotate in a predetermined angular range centered around its axis,
a coil placed outside one end of the main body case in the axis direction, and formed by winding a wire around a bobbin, and
a yoke made of a magnetic material having two ends bent to form an almost U-shaped section, an intermediate portion of the yoke being inserted into the coil, one end of the yoke being placed on one outer side surface of the main body case, and the other end of the yoke being placed on the other outer side surface of the main body case.
Also, as disclosed in Japanese Patent Laid-Open No. 2003-052162, a method has been proposed in which two bearings are used, a yoke is formed into a hook shape, and the two bearings are fixed by the hook of the yoke and a portion to be inserted into a coil bobbin, thereby forming an actuator.
In above-mentioned Japanese Patent Laid-Open No. 10-248231, however, the positioning of the rotor magnet and an arcuate magnetic pole portion of the yoke, which exerts a large effect on the driving accuracy, is performed on only a surface facing the rotor magnet on the outer circumferential surface of the main body case. Also, no method of positioning the two bearings of the rotor magnet has been disclosed. Furthermore, the hook of the yoke fixes the bearings and a cap in Japanese Patent Laid-Open No. 2003-052162. Similar to Japanese Patent Laid-Open No. 10-248231, the arcuate magnetic pole portion of the yoke is positioned on only a surface facing the rotor magnet. In addition, the complicated yoke shape may make the position of the arcuate magnetic pole portion unstable with respect to the rotor magnet.